1. Field of the Invention
The present invention relates generally to an apparatus for controlling an air conditioning unit for an automotive vehicle. More specifically, the present invention relates to the improvement of an apparatus for controlling the air conditioning unit for the automotive vehicle wherein the operation of a compressor is controlled depending upon the operative conditions of the air conditioning unit when an engine speed variation rate is smaller than a predetermined negative value.
2. Description of the Background Art
Generally, with respect to an air conditioning unit for an automotive vehicle, when an air conditioner switch is manually shifted to ON by the driver, or when the switch is automatically actuated in response to the temperature as is often the case with automatic air conditioning units, a compressor is operatively connected to an engine via an electromagnetic clutch so that the compressor starts operation for the purpose of cooling. If the engine speed is reduced to a low level, e.g., an engine idle speed, during the operation of the compressor, an engine idle speed control system provided in an air intake system carries out the first idle control for increasing the engine speed up to a first engine idle speed to prevent the drop in the engine speed. One example of the aforementioned control system is disclosed in an official gazette of Japanese Laid-Open Patent No. 200038/1984.
With respect to the conventional air conditioning unit, when the electromagnetic clutch is connected, the load of the compressor is immediately imposed on the engine. Therefore, the engine idle speed control system opens a throttle valve to increase the air flow rate and at the same time increases a quantity of fuel to be fed to the engine for increasing an engine torque. However, this leads to the problem that there is a delay in the engine speed increasing up to the first idle speed. To obviate the foregoing problem, it has been proposed that a controller carries out the first idle control when the switch is shifted to ON and then operates the compressor after the controller detects the increase of the engine speed in order to prevent the engine speed from dropping. However, in the case where the engine speed is reduced from a high level according to racing or disconnecting a main clutch during running of the vehicle, the controller carries out the first idle control at the same time the compressor begins operating, since the engine speed is still high when the switch is shifted to ON. Therefore, the engine speed is substantially dropped due to delay of the generation of the engine torque by the first idle control. Consequently, another problem or malfunction, such as, engine stop, vibration and, incomplete drivability arises. If the switch is shifted to ON under such operative conditions as described above, it becomes necessary to take an adequate countermeasure for preventing the engine speed from dropping.
To shorten such a delay of the first idle control as described above, several solutions have been proposed such that the weight of a flywheel is increased to retard the drop of the engine speed and that the volume of the intake air system is reduced to increase the response of the first idle control. However, the former proposal has a problem in that the response may be degraded excessively while the latter proposal has another problem that the ending performance of the engine output and the engine layout are adversely affected.
In case where the controller carries out the control such that the compressor starts its operation with delay after the completion of the first idle control, a malfunction, e.g., the over running of the engine tends to occur and thereby it becomes difficult to correctly set time delay due to the dimensional and functional differences in production lots of the engine.